124 
++ Central spine shorter than the radials, 
Radials 5 to 9, stout. 
meiacanthus (7). 
Radials 9 to 22. 
heyderi (5), hemispharicus (6), gummiferus (8), gabbii (34), spharicus (35). 
*** Central spine solitary and hooked. 
+ Stems slender cylindric: Lower Californian, 
Centrals 1, 20 to 30 mm, long. 
roseanus (23). 
Centrals 1 to 4, 20 to 50 mm. long. 
setispinus (24). 
++ Stems depressed-globose to ovate, 
Radials 4 to 6, rigid. 
uncinatus (9). 
Radials 8 to 12. 
wrightit (15). 
Radials 15 to 30. 
grahami (19), eschanzieri (21). 
Radials 50 to 60. 
barbatus (18). 
**** Central spines more than one, and none of them hooked. 
+ Slender or sometimes stout cylindrical plants, branching at base: Lower Californian. 
-brandegei (3), setispinus (24), halei (25). 
«++ Depressed-globose tv ovate and stout cylindrical. 
+ Radials few (3 to 12) and rigid: Mexican, 
Radials 3: centrals 3, 
alternatus (1). 
Radials 7 or 8: tubercies 40 to 50 mm. long. 
longimamma (36). 
Radials 10 to 12: tubercles 12 to 15 mm. long. 
gummiferus (8). 
++++ Radials numerous (16 to 60), capillary or bristle-like. 
Radials 15 to 30, slender but rigid (bristly). 
acanthophlegmus (2), densispinus (4), bispinus (14), rhodanthus (26), sulphure- 
dspinus (27), palmeri (29), pringlei (32). 
Radials 30 to 60 or more, mostly capillary. 
tetrancistrus (22), capillaris (28), teranus (31), sphwrotrichus (33). 
***** Central spines more than one and but one of them hooked, 
Radials 10 to 15. 
goodrichii (16), setispinus (24). 
Radials 15 to 30. 
pondii (17), grahami (19), bocasanus (20), 
Radials 30 to 60. 
tetrancistrus (22). 
